And since May is melanoma month, we thought it was fitting to raise awareness of this deadly disease (and prevent getting burned) by asking Debra Jaliman, M.D., a cosmetic dermatologist in NYC and author of Skin Rules: Trade Secrets from a Top New York Dermatologist, for her thoughts on the six sunscreen mistakes (c/o La Roche-Posay) you could be making without even knowing it:

1. You think you're exempt from sunscreen because you have dark or olive skin. "Even with dark skin you can burn and get sun damage. People with blue eyes and fair skin tones are more prone to skin cancer, but we're all susceptible to it. No matter what skin color you are, you're not exempt from skin cancer or from using sunscreen."

2. You don't apply sunblock often enough. "A lot of people never reapply their sunscreen after putting it on the first time. Also, they tend to wear water-resistant formulas because they think it will stay on through a day of swimming and sweating, but that isn't true. Your SPF should be reapplied every two hours and you should always do the old shot glass trick. Filling up a shot glass with sunscreen and then applying that amount from the neck down will cover and protect you properly."

3. You neglect to wear sunscreen while driving or working indoors. "Through window glass, UVA light comes in and causes premature aging, skin damage, and possibly skin cancer, which means anywhere there are windows you're exposed. Even when you're simply walking from the parking lot to work or to the mall, etc., you're atill at risk of incidental exposure. Five minutes a day of exposure to the sun throughout the course of a lifetime adds up."

4. You use a sunscreen that blocks only UVB rays. "UVB rays are the ones that cause you to burn, while UVA rays are the very deeply penetrating ones that are even more dangerous because they cause damage without you even knowing it. They alter your DNA, eventually bringing on brown and white spots, early aging, broken blood vessels, and uneven texture."

5. You're using a sunscreen that has expired. "What happens, I've noticed, is that the expiration wears off as the sunscreen gets older. You'd never pour a glass of milk without checking the expiration date, right? So why would you use sunscreen that is supposed to protect your skin without checking if it's still good? If the date on the bottle has worn off, or you can't remember when you purchased it, toss it. It won't be effective if you slather it on and it's old, since the molecules decompose and deactivate over time."

6. You miss spots. "People end up getting badly burned on the tip of their nose, the tops of their eyelids, on their ankles, and the back of their knees. Why? They don't apply it in the nude. I always tell my patients to put their sunscreen on before their bathing suit, that way they're more apt to cover their entire body. Especially since some of these beautiful swimsuits have cutouts and straps everywhere—if you miss a spot applying SPF at the beach you're going to get burned."

Are you guilty of making any (or all) of these sunscreen mistakes? If so, we encourage you to take Dr. Jaliman's advice seriously and start practicing safe skin!